Various types of known drive apparatuses are suggested for a hybrid vehicle provided with an engine and with a motor as drive units. For example, the drive apparatus including an input shaft rotatably connected to the engine, an output shaft connected to a rotor of the motor so as to be integral with the rotor, and a clutch device connecting the input shaft to the output shaft in a manner that the input shaft engages with and disengages from the output shaft is known. The output shaft is connected to a transmission directly or via a torque converter, and thus a power train leading to drive wheels is established. According to this structure, the vehicle may run only on the engine or only on the motor, or run on both the engine and the motor when a large drive power is needed. Further, due to energy regeneration while the engine is running or the brake is applied, the motor may be used as a generator and a battery may be charged.
According to the above-described structure, the power train may become larger in size and heavy and a cost may increase in case an individual device is structured independently from one another, and therefore the plural devices are generally incorporated in one case. For instance, the clutch device is incorporated in a motor case so that, for example, oil is used commonly for lubricating and for cooling a bearing of the motor and clutch plates, and for actuating a clutch piston. Other structures in which the plural devices are combined are in practical use, one of which is disclosed in JP2004-180477A (hereinafter referred to as Patent reference 1). In order to supply oil, a method to scoop up the oil by means of a rotating object, for example, a gear, a method to pump the oil by using a mechanical oil pump provided at a rotation shaft or an electric oil pump, and other methods are applied.
According to a cooling structure of a motor of a front and rear wheel drive vehicle disclosed in the Patent reference 1, a single casing accommodates a motor, reduction gears and a differential gear, and oil is used commonly for purposes of cooling and lubrication. According to the Patent reference 1, an oil sump is provided at a bottom of the casing. A static oil level of the oil sump is high while the motor is stopped but a dynamic oil level of the oil sump decreases while the motor is running because the oil accumulates in an oil catch tank and in an oil slinger chamber. In a state where the dynamic oil level is decreased, a drag resistance, that is, the resistance caused when the oil is dragged against a viscosity thereof by the rotating motor, is reduced.
According to the Patent reference 1, an amount of the oil contained in the casing is limited by a condition that the dynamic oil level should not inhibit the rotation of the rotor of the motor. Therefore a sufficient amount of oil may not be necessarily assured. This restriction may also exist in other cases where a clutch device is incorporated in a motor case. The amount of the oil is limited in order to reduce the drag resistance of the rotor, and thus a sufficient amount of oil necessary for the operation of the clutch or other purposes may not be assured.
In addition, the oil sump may be divided by components, for example, a stator, arranged in the case of the drive apparatus into a part that includes an oil intake port communicating with an oil pump and other parts that do not include the oil intake port. In this case, the oil level of the part of the oil sump, which includes the oil intake port, reduces to be lower than the oil level of the other parts of the oil sump, which do not include the oil intake port, and thus the oil pump may not pump a sufficient amount of the oil. Further, the oil level may fluctuate by oscillating in the left and the right directions while the vehicle is making a turn, which may be undesirable in terms both an increase in the drag resistance of the rotor and a reduction in an amount of the oil pumped by the oil pump.
The amount of oil contained in the case may be increased by increasing the dimensions of the case of the drive apparatus or by additionally providing a sub tank, however, case having the larger dimensions or the additional sub tank may interfere with peripheral parts and components when the drive apparatus is mounted on the vehicle. In addition, a cost of the drive apparatus may increase.
A need thus exists for a drive apparatus for a vehicle and a case thereof, which is not susceptible to the drawback mentioned above.